Hmm your story just indicates "problems"... nothing like what I thought.

I am confident now that many mechanics don't know **** about electrics and electronics. And that includes those who work on Murena's for living.

Speaking of problems, there is an oil leak coming from the top of the engine, between the 1st and 2nd cylinder. Those are signs of the cylinder head gasket starting to fail, a mechanic told me Also, I am not really happy with the state the rubber hoses of the cooling system are in.

Hmm your story just indicates "problems"... nothing like what I thought.

I am confident now that many mechanics don't know **** about electrics and electronics. And that includes those who work on Murena's for living.

Speaking of problems, there is an oil leak coming from the top of the engine, between the 1st and 2nd cylinder. Those are signs of the cylinder head gasket starting to fail, a mechanic told me Also, I am not really happy with the state the rubber hoses of the cooling system are in.

What are the signs? Coolant in the oil? Oil in the coolant? What is the state of the spark plugs in these cylinders?

If it's on the back (exhaust side) of the engine, then check the rocker cover gasket: If the oil is also above the head gasket, then that's probably the source. It can leak, and if it fails the leak can be quite dramatic. The fix is easy though! I had this problem exactly one year ago (Lennart, Roy will remember )

I think the bulb is 1.5W, i.e. about the same resistance as the resistor, and as they are wired in parallel you should get some 30-50 Ohm on your multimeter if you are measuring from the alternator.

No, the bulb is 1.2 watts. The 82 ohm resisitor is roughly equivalent to the 2.2 watt bulb manufacturers always used to use for insturment warning lamps. (if you use 13.4 volts which is minimum charging voltage and since R=V squared/W the resistance is 81.62 ohm) Now it could be that they designed this to energise the alternator if the bulb was blown as you suggested, but I don't see why they would do this since no other manufacturer has ever done this to my knowledge and with the bulb blown you have no quick or visual indication of any problem. The real reason will probably never be known unless you could find the person who designed it and asked them!

Since the bulb should always be in balance with the system charging, the same voltage one side (from the battery) as the other (the alternator) if the bulb glows it shows there is no longer a balance and one side is higher than the other, causing a current flow. If it is the alternator which is higher it signifies over-charging, something people often forget - they always tend to assume the light on means under-charging. Now as the Murena battery condition gauge reads low, if it was slightly over-charging the gauge could be a little higher than usual but you might not realise you had a problem if you had no bulb. So putting a resistor in to allow the system to run without a bulb is a bad idea. Over-charging damages the battery and often electronic components.

Also, when I investigated a Bagheera that wasn't charging correctly, the only problem turned out to be the bulb was missing! As soon as I replaced the bulb, it charged correctly, suggesting that it required both to energise correctly.

The bulb and resistor in parallel should give you roughly 49 - 50 ohms at 12 volts

Self energising alternators require nine diodes as opposed to six for normal ignition energised alternators. More importantly if you used a self energising alternator, you would need a means to switch off the supply when the engine was off otherwise the current drain through the alternator would drain your battery, and you would need a separate warning light control unit. We used to use these 3AW (warning light control) units years ago on BMC vehicles when we did use self energising alternators! I can't think of any cars with self energising units today.

I have done some measurements yesterday.When the ignition is switched off, the ignition warning light circuit reads about 30 ohm between #9 wire and chassis ground.If I switch the ignition on and connect the igntion warning light to ground, the warning light goes on. But it doesn't come on once I connect the #9 to the wire which should be the #9 wire.

What is the grey wire with red connector seen in this picture. Is that the #9 wire (charging warning light)?

What is the grey wire with red connector seen in this picture. Is that the #9 wire (charging warning light)?

No an original grey wire with red marker is a permanent ignition wire (No.10)(The problem is with your altered wiring you cannot rely on anything. You may have to check where every one actually goes)The warning light wire should be red with green marker (No.9)The red wire with yellow marker goes to the diagnostic socket (No.8)Large red wires are live to battery/starter (No.1)And there should be a black earth wire (110C)

You might also have a radio suppressor which would be bolted to the earth point with a small wire connected to the live connection (1).

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I am confused, I can only find the permanent +12V and that grey wire...

You need to find out what they have done with the red wire with green marker (9). Someone might have removed the end, and lost the green marker and assumed as it is red that it is the same as the live wires. It is not. The same applies to the red wire with yellow marker that only goes to the diagnostic socket. Separate all red wires and check them individually.

From your photo it looks like you have no wire connected to the warning light connection. The connection is the second small connector in the socket where your grey wire is connected. There should have been a plug on the loom with two wires in it, to connect in to that socket and the other terminal slightly below your grey wire, is the warning light connection.

You need to find out what they have done with the red wire with green marker (9). Someone might have removed the end, and lost the green marker and assumed as it is red that it is the same as the live wires. It is not. The same applies to the red wire with yellow marker that only goes to the diagnostic socket. Separate all red wires and check them individually.

OK, I will do that! This might explain why there are a couple of loose connectors hanging around.

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From your photo it looks like you have no wire connected to the warning light connection. The connection is the second small connector in the socket where your grey wire is connected. There should have been a plug on the loom with two wires in it, to connect in to that socket and the other terminal slightly below your grey wire, is the warning light connection.

Could it have done damage to the alternator if I have accidentally swapped the wires in that socket, i.e. the #10 to the warning light connection?

By the way, what purpose has the #8 wire to the diagnostic socket? The #1 and #10 wires are also present there, so it must be something else... And if the #9 and #10 wires go to that small socket mentioned earlier, where should the #8 go?

And is it a good idea if I run the #9 directly to the alternator, instead of through the engine wiring loom (which I do not trust)

It's there to diagnose faults on the alternator itself, specifically the regulator. It's all described in the workshop manual, but requires a bit of electronics knowledge. You can easily live without it.

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And is it a good idea if I run the #9 directly to the alternator, instead of through the engine wiring loom (which I do not trust)

It shouldn't make any difference if you can ensure there is a connection and there are no short circuits. If you don't trust the loom, I suggest you take it out of the car completely and restore it. Getting it free of the tabs under the inlet manifold is a bit difficult as far as I can see though, unless you unscrew the manifold from the head of course. But maybe it is possible to do that without detaching the coolant hoses, though it may be necessary to take the carburettor off. What do you think, Roy?

OK, I will do that! This might explain why there are a couple of loose connectors hanging around.

Yes, I wondered about those.

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Could it have done damage to the alternator if I have accidentally swapped the wires in that socket, i.e. the #10 to the warning light connection?

Not sure, but if you think that the warning light wire would have no voltage only current, since the bulb will have taken the voltage; whilst the ignition wire will have full voltage, there is a possibility.

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By the way, what purpose has the #8 wire to the diagnostic socket?

As Anders has pointed out, it is purely for diagnostics, so if you never use it then it is not important if you don't have it connected.

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... where should the #8 go?

It attaches to the main red terminal (No.1)

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And is it a good idea if I run the #9 directly to the alternator, instead of through the engine wiring loom (which I do not trust)

Yes, you can run it directly, just as long as it is not going to get trapped, or caught or rubbed through by anything. Getting the engine loom out without stripping is always difficult. The standard down-draught carb. manifold should have a support bolted to the bottom of it, going to the block. This is difficult to get at and makes the manifold difficult to remove, as it is not only bolted to the head. However, ideally it would be best to remove and remake the engine loom, but you have to weigh up the work against the need, and risk.

Could it have done damage to the alternator if I have accidentally swapped the wires in that socket, i.e. the #10 to the warning light connection?

Not sure, but if you think that the warning light wire would have no voltage only current, since the bulb will have taken the voltage; whilst the ignition wire will have full voltage, there is a possibility.

The good news: I managed to get the engine working and the alternator is charging, with a functioning warning light! (that is, it goes black when the engine is running and lights up when the engine is not running) The car passed the APK (MoT) flawlessly and it should be ready to roll.

However, I had some things to finish.

The bad news: while I was busy replacing the #10 wire behind the dashboard (if I'm correct, the ignition switched battery voltage goes to the engine, to the fuse board and to the interior fan), I did yet another horrible discovery. The +12V connector and the connector to the second position (the one I'm using most of the time) were completely rotten, the latter literally fell apart when I was trying to pull it off the switch!

Ceci n'est pas un commutateur...

c'est un art du bruler!

Well, at least I know where the smoke came from when my car died two months ago! I hope I can find some kind of replacement, there is an old electronic parts store in town here (the last of the Mohicans), or else I should source one from Carjoy or Simon, because this one is too far gone I'm afraid.

What fuse shall I use to protect the fan switch circuitry? Will 20A suffice?

Years ago my car had a leaky sunroof, which often caused the interior to become damp, and I assumed this humidity accelerated the deterioration of various things - including the connectirs on the switch. But the main reason is probably that it per design gets warm when the fan is on (which it normally always has to be). So after 20 years of warming up/cooling down, the corrosion has easy play.

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What fuse shall I use to protect the fan switch circuitry? Will 20A suffice?

dunno, - I replaced the switch with a new one from MatraMagic, and it hardly gets warm at all, so I haven't thought about fitting a fuse. I don't think my melting switch was pulling more amps than usual, - it was just being burned off in the switch instead of the fan motor.

Having said that, it still might be a good idea, and considering the not-so-impressive power of the fan, I'd think 20-30A should suffice.

Could it have done damage to the alternator if I have accidentally swapped the wires in that socket, i.e. the #10 to the warning light connection?

Not sure, but if you think that the warning light wire would have no voltage only current, since the bulb will have taken the voltage; whilst the ignition wire will have full voltage, there is a possibility.

The good news: I managed to get the engine working and the alternator is charging, with a functioning warning light! (that is, it goes black when the engine is running and lights up when the engine is not running) The car passed the APK (MoT) flawlessly and it should be ready to roll.

Hoooray!! Very good news, indeed.

About the fan switch... I'm about the fuse that myself as soon as I get a spare evening to fit the ignition relay I have complete with harness lying on my workshop table... I'm going to try a 15A fuse. I'm sure that is enough, after all it is a relaitvely small fan.

A switch on an inductive load (like a motor) is bound to give problems in the long run, but you can hope that the run is very long. However, as long as it works, the problem isn't great, the problem comes when the contacts get so dirty that they give a resistance - the switch will then get hot as current is drawn through it.

The solution to the problem is to fit a diode in reverse over the switch. That will short circuit the induced current instead of creating sparks inside the switch.

I had the heater problem only a month or two ago... good thing you discovered it before it caught fire..... My first warning that something was wrong, was when smoke came pouring out from behind the dashboard ..!

I have a 10 amp fuse in the pre-heater feeding the fan. It works, so 10 amp will do.

But beware. fusing things is no guarantee for safe electrical system. Example: The fan is now fused with 10 amps. So if the fan circuit takes more than 10 amps, fuse blow, everybody happy. But what happened to brinkie and krede is a bad connection on the switch. This is not a short or overload circuit! If this bad connection has a resistance of 0.1 ohm, and the fan takes 10 amp, than the power it generates in this bad connection is 10 watt! 10 watt doesn't sound as a lot but 10 watt can generate enough heat to melt things or worse.